Prof. Hyunyong SHIN would like to share the attached article that deals with the number line as a visual representation of the real number system.

Abstract:

Abstract Number line is a visual representation of real number system. There was no arrow at eitherend of the representation in the early figures of number line. But after the 19th century, number lines with one arrow on the right hand side have begun to appear. In USA, however, many textbooks of secondary school mathematics have number lines with arrows on the left hand side as well as on the right hand side. It is quite different from the global standard. We argue that it is mathematically reasonable for number lines to have an arrow only on the right side.